One of the fastest methods of screening a large number of people or items for the presence of explosives or drugs on them is to draw a sample of air across each person or item and then see if the air contains explosive particles or drug residue. This is a quick, non-intrusive, and effective method of determining if the person or item has been in contact with explosives or drugs.
A problem arises, however, in testing and calibrating the device which is used to measure the presence of the substance of interest. The problem is in duplicating the way that the substances get placed on and released from the surfaces of items touched by terrorists such as luggage handles, packages, etc. and their clothing. In addition, the amount of explosive or drug on a person or item differs if the person or item has had substantial contact (i.e. the person has manufactured an explosive device or been directly involved in a drug transaction) or only casual contact with the substance (i.e. money that was in a bank drawer and came in contact with other money that had been used in a drug transaction or handled by someone who had been working with explosives). This latter requires the development of test samples having different (known) levels of explosives or other substances on them.
The prior art method was to make a liquid suspension of the explosive or other substance of interest, then apply this suspension to an item. After the suspension had dried, the item was then passed through the detection portal where an air sample was taken and analyzed for the presence of explosive particles or drug residue. The problem was that if the explosive or drug had been deposited on a rough or textured surface it would settle in the grooves of the surface, and very little would be drawn into the sampled air. Thus the detector would fail to report the presence of explosives or drugs in an unacceptably high number of cases. If the suspension were applied to cloth, the particles would be carried between the fibers of the cloth by capillary action and would not be picked up by the air stream, again resulting in a false negative report.
Accordingly, it is an object of the present invention to provide a method of preparing test samples that simulate the properties of real items that contain minute-quantities of explosives or drugs on their surfaces.
It is a further object of the present invention to provide such a method wherein the quantity of explosive or drug can be varied.
It is a further object of the present invention to provide such a method which is quick and easy and which produces reliable results.
Briefly, the present invention comprises the steps of preparing a liquid containing the explosive or other substance of interest, placing some of the liquid on a Teflon(copyright) coated surface, allowing the liquid to dry, and then rubbing the coated Teflon(copyright) on an item, thereby transferring the explosive or other substance of interest to the surface of the item.